In recent years, as image-recording materials, materials for forming color images have been predominant and, specifically, recording materials for an inkjet system, recording materials for a thermal transfer system, recording materials for an electro-photographic system, transfer type silver halide light-sensitive materials, printing inks, and recording pens have found widespread use. Also, in photographing devices such as CCDs for photographing equipment, and in LCDs and PDPs for display, color filters are used for recording or reproducing a color image. In these color image recording materials and color filters, colorants (dyes or pigments) of three primary colors of a so-called additive color mixing process or subtractive color mixing process have been used in order to display or record full-color images. In actuality, however, there is no fast colorant having the absorption characteristics capable of realizing a preferred color reproduction region and resisting various use conditions and environmental conditions. Thus, the improvement thereof has strongly been desired.
Dyes or pigments to be used for the above-mentioned uses are required to have in common the following properties. That is, they are required to have absorption characteristics favorable in view of color reproduction and have good fastness under the conditions of the environment wherein they are used, for example, fastness against light, heat, and an oxidative gas such as ozone. In addition, in the case where the colorant is a pigment, the pigment is further required to be substantially insoluble in water or in an organic solvent, to have a good fastness to chemicals, and not to lose the preferred absorption characteristics shown in a molecularly dispersed state even when used as particles. Although the required properties described above can be controlled by adjusting the intensity of intermolecular mutual action, both of them are in a trade-off relation with each other, thus being difficult to allow them to be compatible with each other.
Further, in the case of using a pigment as the colorant, the pigment is additionally required to have a particle size and a particle shape necessary for realizing desired transparency, to have good fastness under the conditions of the environment wherein they are used, for example, fastness against light, heat, and an oxidative gas such as ozone, to have good fastness to an organic solvent and chemicals such as a sulfurous acid gas, and to be capable of being dispersed in a used medium to a level of fine particles, with the dispersed state being stable.
However, since the azo pigment shows different structural isomerization and crystal polymorphism depending upon the production process, and hence it has been difficult to produce an azo pigment having structural isomerization and crystal polymorphism capable of exhibiting desired characteristics with high reproducibility and high purity.
In JP-A-4-227765, a process for producing a yellow pigment by conducting diazo coupling by adding a diazonium salt solution to a suspension of a coupling component or in an aqueous medium at a pH of 7 or less is described.
Also, in JP-A-2009-73978, a process for producing an azo pigment by conducting coupling reaction between a diazonium compound prepared by diazotizing a heterocyclic amine and a heterocyclic amine in the presence of sulfuric acid.
However, there has strongly been desired a process for producing, with high efficiency, a pigment having more purity, showing good hue, having high tinctorial strength (coloring power), and having high fastness against light, moist heat, and active gases in the environment.